PHOSPHATE ROCK. 



BY JOSEPH STRUTHERS. 



[Joseph Struthers, mineralogist; born at New York city in 1865, and attended 

 the School of Mines, Columbia college (now Columbia university), graduating in 

 the course of chemistry in 1885; for fifteen years after his graduation he was on the 

 staff of instructors of the department of metallurgy at Columbia university; organ- 

 ized and conducted the first summer school in practical metallurgy of Columbia 

 university (1896), which was at Butte, Mont. Dr. Struthers has visited many 

 metallurgical plants in the United States and Europe, and he has carried on special 

 metallurgical investigations; he has written numerous articles for the Engineering 

 and Mining Journal, Mineral Resources of the United States, Twelfth Census of the 

 United States and School of Mines Quarterly, and is assistant editor of the Transac- 

 tions of the American Institute of Mining Engineers; appointed Field Assistant to 

 the United States Geological Survey for 1901 and 1902, and in May, 1903, special 

 agent for the United States census.] 



The name phosphate is applied to the salts of phosphoric 

 acid, chiefly orthophosphoric acid, which is a tribasic acid 

 (H3PO4) and from which a great variety of salts are obtained. 

 Each of the three hydrogen atoms in the acid can be replaced 

 by a monad element, forming consequently, three varieties of 

 salts, namely, those in which one hydrogen atom is replaced, 

 those in which two hydrogen atoms are replaced, and those in 

 which all of the hydrogen atoms are replaced. Salts in which 

 all of the hydrogen atoms have been replaced are called ortho 

 or neutral phosphates, while those still containing one or two 

 atoms of hydrogen are called acid phosphates. Calcium phos- 

 phate, or more strictly speaking, tricalcium orthophosphate, 

 is the most important of the mineral phosphates and this class 

 forms the large mineral deposits utilized for the manufacture 

 of fertilizers. 



According to historical records, the Romans utiHzed the 

 excrement of birds for fertilizing the soil, and in the twelfth 

 century the Arabs and Peruvians used the guanos of their 

 respective countries for a like purpose 



The waste clippings of bone and ivory from the button 

 and knife factories of Sheffield, England, greensand from the 

 counties of Kent and Essex, England, marls from the state of 

 New Jersey, and boneblack (spent animal charcoal) and crush- 

 ed bones were used as fertilizers, at different times during the 

 eighteenth and nineteeth centuries, but while the beneficial 



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